Physics of auroral phenomena : proceedings of the 36th Annual seminar, Apatity, 26 February – 01 March, 2013 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2013. - 215 с. : ил., табл.

N. V. Zolotova and D.I. Ponyavin S(ln+\,tn+\) + S(ln+i - v •(?„+, - tn),tn), where y is velocity of meridional flow depending on latitude. Fig. le illustrates that each activity impulse causes poleward surges. Actually, each impulse can generates both old and new polarity waves, but impulse geometry and their overlapping in time and latitude suppresses old polarity surges ( Zolotova and Ponyavin, 2012a). Thereby, the poleward streams of old polarity are usually observed in gaps between impulses (see cycle composed of three impulses, Fig. le). where 1 '0 = 13 m s >/Q= 1 3 . 3 ° ^ = l, q = 0 . 1 , see green dashed line on Fig. 2. Additionally, to test we used two latitudinal profiles of latitudinal separation: Ad = 10° - orange solid line; Ad = 8 ° - orange thin line. Time jyoorj Fig. 1 (a) The cycle activity: number of BMRs per day — grey color, 6 months moving average — black color, (b) Modeled butterflies of individual BMRs. Yellow and blue define polarities, (c) Probability density function for BMRs. The color marks the levels o f equal point density, (d) Surplus for modeled butterflies fox Ad = 10° and l’o = 13 m s ’ 1 at latitude 45°. (e) Reconstructed surges. P a r a m e te r s tu d y There are different approaches making use of latitude at which the meridional flow speed u reaches a maximum: - 10°-20° ( DeVore & Sheeley, 1987; Wang et al., 2009; Dikpati et al., 2010): uG>= U p S i n ^ / j J , where l'o = 13 m s*1, /0 = 90 0, see green dotted line on Fig. 2; -- 35°-50° ( van Ballegooijen et al., 1998; Schrijver & Title, 2001; Jiang et al., 2011b; Hathaway & Rightmire, 2011): Fig. 3 illustrates parameters study for the RGO/USAF/NOAA daily data set from 1875 to 2012 (Zolotova and Ponyavin, 2013). Impulses are derived from sunspot positions ( http://solarscience.msfc. nasa.gov/greenwch.shtml) by means of averaging of sunspot distribution on time-latitude plane (Fig. 3a). Colors denote equal levels of density. Parameters of sunspot impulses tracing are average window dl*dt = 0.6x1 and iteration step i - 20. Equal levels of density denote that populations of sunspot during the cycles 19, 2 1 , and 2 2 are the highest. Fig. 3b displays reconstructed magnetic poleward surges in dimensionless units SKt:sM(l,t). In absence of background field and diffusion, each surge reaches polar latitudes. Flux surplus of leading polarity is evident at low latitudes, similarly to the real photospheric patterns (Hathaway, 2010). Fig. 3c demonstrates smoothed over 10 Carrington rotations values of SRssuU(l,t) at latitudes 80° and -80°. Used parameters are Ad = 10° and l'o = 13 m s' 1 at latitude 45°. Gleissberg cycle is evident (Gleissberg, 1967). Also from the Wilcox Solar Observatory (http://wso.stanford.edu/) it is known that magnitude of polar field decreases from cycle 2 1 to cycle 23. Similar regularity can be seen in Fig. 3c. Fig. 3d illustrates the same values of SResu|t(/,0, but constructed for the following parameters: Ad = 10° and l'o = 13 m s ' 1 at latitude 13.3°. Magnitude of surges reaching the poles is reduced by almost half. Fig. 3e shows the same values of 5ResuU(/,?) for Ad = 8 ° and l’o = 13 m s ' 1 at latitude 45°. Magnitude of surges is slightly reduced. Finally, both an increase of the meridional flow speed toward the equator and vanished slope of tilt angle of BMRs against the latitude reduce strength of surges. However results depend on the size of mesh grid. Wang et al. (2002a) observed that the strongest poleward surges occur near and just after sunspot maximum and are accompanied by fluctuations in the polar fields. Wang et al. (1989) suggested that such surges are generated by a combination of enhanced activity and large meridional flow speeds. We latitude, degree Fig. 2 Latitudinal profiles: meridional flow (green dotted and dashed), latitudinal separation Al (orange solid and thin). 131